Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent: II. GA3 increases yield and fruit size of ‘Hass’ avocado only in the on-crop year of an alternate bearing orchard

For studies on blossom/fruit thinning in apple, tree selection is often based on uniformity of bloom/crop load, assuming that such trees exhibit greater uniformity to treatment. However, the literature is replete with data showing marked variation for a given treatment. We followed variation in bloom/crop density of spur-type `Delicious'/MM.106 and effect of ethephon applied in high crop years on return bloom/yield. Uniform trees (n = 95), under identical cultural practices, were selected for varying crop load. Return bloom, yield and fruit size were monitored over six years. General mean (X) for yield was 94 ± 25 kg/tree and bloom density, rated 1 to 10 (highest), was 5.4 ± 1.7. Annual yield deviated from X by +56 to –40% and bloom density by +49 to –42%. All trees were ranked (decreasing yield) and assigned to five percentile (PCTL) groups (1st, 81-100; 2nd, 61-80; 3rd, 41-60; 4th, 21-40; 5th, 0-20 kg/tree). Trees in each group were reassigned annually to the five PCPL groups for the next five years. Of trees in 1st PCTL (n = 19, X = 187 ± 10 kg/tree) in year one, 5, 5, 24, 0 and 63% placed in PCPL 1, 2, 3, 4, and 5, respectively, in year two. Of trees in 1st PCTL (5%) in year two, all placed in PCTL 2 in year three. Effect of ethephon [200 mg·L-1 at 3, 3 + 6, 3 + 6 + 9 weeks after full bloom (WAFB)] applied in on years to `Redchief', with strong alternate bearing, were evaluated for six years. Ethephon at 3 WAFB had no effect. Yield from multiple applications differed from control (NTC) in off years, but not from each other. Total yield (3 on + 3 off years) for the NTC and ethephon at 3 + 6 WAFB was similar (479 vs. 471 kg/tree). However, 64% of the total yield was produced in the on years and 36% in the off years in NTC vs. 56 and 44% in 3 + 6 WAFB, respectively.

Download Full-text

Foliar-applied GA3 Advances Fruit Maturity and Allows Off-season Harvest of ‘Hass’ Avocado

HortScience ◽

10.21273/hortsci.42.2.257 ◽

2007 ◽

Vol 42 (2) ◽

pp. 257-261 ◽

Cited By ~ 1

Author(s):

Samuel Salazar-García ◽

Luis E. Cossio-Vargas ◽

Isidro J.L. González-Durán ◽

Carol J. Lovatt

Keyword(s):

Gibberellic Acid ◽

Foliar Application ◽

Fruit Size ◽

Inflorescence Development ◽

Avocado Fruit ◽

Negative Effect ◽

Effect On Yield ◽

Hass Avocado ◽

Vegetative And Reproductive Growth ◽

Prohexadione Calcium

Michoacán and Nayarit are, respectively, the largest and second largest avocado-producing states in Mexico. The main harvest of the ‘Hass’ avocado in both states is concentrated during November to December, which saturates the market and reduces the price of fruit and grower income. The goal of this research was to manipulate vegetative and reproductive growth of the ‘Hass’ avocado with properly timed foliar-applied plant bioregulators (PBRs) to shift the date of flowering and harvest to the period before or after the main harvest. Effects of canopy sprays of gibberellic acid (GA3) or prohexadione calcium (a gibberellic acid biosynthesis inhibitor) applied at different stages of tree phenology on inflorescence development, time of anthesis, date of legal maturity for harvest of ‘Hass’ avocado fruit, yield, and fruit size were quantified. No PBR treatment influenced the time of anthesis. A single or double foliar application of GA3 (50 mg·L−1) ≈4 months (July) before the expected date of main harvest (November) resulted in ‘Hass’ avocado fruit reaching legal maturity (mesocarp dry matter 21.5% or greater) 24.8 to 28.2 d earlier than those of untreated control trees with no negative effect on yield or fruit size.

Download Full-text

Gibberellic Acid Inhibits Flowering and Reduces Hand Thinning of `Redhaven' Peach

HortScience ◽

10.21273/hortsci.41.7.1596 ◽

2006 ◽

Vol 41 (7) ◽

pp. 1596-1601 ◽

Cited By ~ 7

Author(s):

Elina Coneva ◽

John A. Cline

Keyword(s):

Gibberellic Acid ◽

Prunus Persica ◽

Fruit Size ◽

Soluble Solids ◽

Fruit Firmness ◽

Cross Sectional ◽

Crop Load ◽

Current Season ◽

Time Of Application ◽

Novel Approach

Adjusting the crop load of peaches [Prunus persica (L.) Batsch] by hand thinning is currently required to ensure marketable size of most cultivars grown in Ontario. A novel approach to adjust cropping by inhibiting flowering using gibberellic acid (GA3) was tested in an orchard experiment in which GA3 was applied at 7, 10, and 13 weeks after full bloom to mature `Redhaven' peach trees. Late GA3 treatments increased soluble solids concentration (SSC) in the season of application. A significant interaction between GA3 rate and time of application was observed on increased fruit firmness in the current season. Increasing rates of GA3 decreased flowering the following season in a quadratic fashion, resulting in a 41% to 90% diminished requirement for hand thinning. This translated into lower crop loads and yields for GA3-treated trees at harvest compared with untreated control trees. However, GA3-treated trees had larger mean fruit size and improved fruit size distribution the year after GA3 application. Advanced fruit ripening was also evident by increased fruit SSC and decreased fruit firmness, likely an indirect effect of GA3 on crop load. GA3 application timing significantly increased overall tree growth measured by the changes in trunk cross-sectional area.

Download Full-text

Bloom Thinning of Peaches with Gibberellic Acid in the Southeast

HortScience ◽

10.21273/hortsci.33.3.514b ◽

1998 ◽

Vol 33 (3) ◽

pp. 514b-514

Author(s):

Michael L. Parker

Keyword(s):

Gibberellic Acid ◽

Fruit Size ◽

Peach Fruit ◽

Crop Load ◽

Application Rates ◽

Short Shoots ◽

Capital Intensive

Thinning peach fruit in the spring of the year is one of the most labor- and capital-intensive operations for peach growers in the southeast. In addition, fruit size can be negatively affected if peach thinning is delayed. The objective of this study was to evaluate the application of gibberellic acid (4% GA3, Ralex—Abbott Labs) in June to reduce peach bloom the following spring. Ralex was applied in June 1995 and 1996 to `Contender' peaches. Bloom density was evaluated in Spring 1996 and 1997 from long and short shoots from the higher and lower portions of the tree's canopy. Applications in 1995 were to trees with a crop load while applications in 1996 were to trees without a crop due to a spring freeze. Bloom densities in 1997 were 300% greater than bloom densities in 1996. The five rates of material evaluated were 0, 59, 79, 99, and 119 g/ha. In 1996, bloom density was significantly reduced with Ralex applications with the greatest reduction with the 99 and 119 g/ha application rates. However, in 1997 only slight differences were detected between all treatments with no difference between the control and 79-g/ha rate.

Download Full-text

Mechanical Crop Load Management (CLM) Improves Fruit Quality and Reduces Fruit Drop and Alternate Bearing in European Plum (Prunus domestica L.)

Horticulturae ◽

10.3390/horticulturae6030052 ◽

2020 ◽

Vol 6 (3) ◽

pp. 52

Author(s):

Sebastian Lammerich ◽

Achim Kunz ◽

Lutz Damerow ◽

Michael Blanke

Keyword(s):

Fruit Quality ◽

Sugar Content ◽

Fruit Size ◽

Load Management ◽

Alternate Bearing ◽

Crop Load ◽

Fruit Drop ◽

Small Fruit ◽

Class 1 ◽

Slender Spindle

(1) Background: With ca. 10 million tons of annual production worldwide, the plum (Prunus ssp.) ranks as a major fruit crop and can suffer from small fruit size, premature fruit drop and alternate bearing, which are addressed in this paper using a range of crop load management (CLM) tools. (2) Methods: Sixty 10-year-old European plum cv. “Ortenauer” trees on dwarfing St. Julien INRA GF 655/2 rootstock (slender spindle; 4.25 × 2.80 m) in a commercial orchard near Bonn (50°N), Germany, were thinned in 2 years and flower intensity assessed in the following year. Thinning was performed either mechanically (type Bonn/Baum) or chemically, with ATS (ammonium thiosulfate) or ethephon (Flordimex), or by a combination of mechanical and chemical methods, to improve fruit quality and the proportion of Class 1 fruit. Adjacent un-thinned trees served as controls. (3) Results: Natural fruit drop in June was reduced from 290 fruits per tree in the un-thinned controls to 265 fruits after ATS blossom treatment, and to 148 fruits after mechanical thinning at 380 rpm at a 5 km/h tractor speed at full bloom. The un-thinned control trees developed a large number of small, undersized fruits. The yield of Class 1 fruits increased per tree from 47% in the un-thinned controls, up to 69% after crop load management. Sugar content and fruit firmness were unaffected. (4) Conclusions: The study has shown that fruit quality (i.e., fruit size) and financial returns could be improved by either mechanical (380 rpm at 5 km/h) or chemical thinning, or a combination of both.

Download Full-text

Interaction Between CPPU and NAA on Fruit Thinning and Fruit Development in Selected Apple Cultivars

HortScience ◽

10.21273/hortsci.33.3.513c ◽

1998 ◽

Vol 33 (3) ◽

pp. 513c-513 ◽

Cited By ~ 1

Author(s):

Martin J. Bukovac ◽

Jerome Hull ◽

John C. Neilsen ◽

Michael Schroeder ◽

Georg Noga

Keyword(s):

Total Yield ◽

Fruit Size ◽

Frost Damage ◽

Fruit Growth ◽

Soluble Solids ◽

Seed Number ◽

Crop Load ◽

Fruit Thinning ◽

Carpel Development ◽

Return Bloom

NAA is used extensively for fruit thinning of apples to increase fruit size and to promote return bloom. In some cultivars, even if thinning is achieved, fruit size at harvest may be less than expected based on crop load. CPPU, N-(2-chloro-4-pyridinyl)-N.-phenylurea, has been shown to increase fruit growth in apples, grapes, and kiwi. We evaluated combinations of NAA and CPPU on thinning, fruit growth and return bloom in Redchief `Delicious', `Elstar', and `Gloster'. CPPU was applied at 5 mgμL–1 (based on 0 to 10 mgμL–1 response curve) in combination with 15 mgμL–1 NAA as high-volume sprays at 7 to 10 mm KFD. Yield and fruit size distribution (on total yield) were used as index of response. In `Delicious', CPPU (3-year study) increased % large (70 mm+) fruit, but in the presence of NAA % large fruit was reduced 2 of the 3 years. CPPU did not induce significant thinning. There were no significant effects on color or soluble solids; firmness was increased slightly and seed number reduced. The L/D ratio was increased and uneven lobe and carpel development was common. CPPU had no significant effect on return bloom in presence or absence of NAA, but NAA increased bloom in both the presence and absence of CPPU. With `Elstar' (2-year study) there was no significant thinning with either chemical, but CPPU increased mean fruit size and % large (70–80 mm) fruit over nonthinned, but not significantly greater than NAA alone. There were no significant differences in firmness, color, soluble solids or seed number. NAA + CPPU did not inhibit fruit growth or cause excessive uneven carpel development. Frost damage reduced crop load in `Gloster' where results were similar to `Elstar' except seed number was reduced by the NAA + CPPU combination.

Download Full-text